Fix regression caused in e553e9e4

In the process of converting the assembly from AT&T syntax to Intel
syntax, bjorn3 made some mistakes. Firstly, `A+B(%reg)` is translated to
`[reg + A + B]`, and not `[reg * B + A]`. I can see how this was
confused because x86 also has an addressing mode that takes up to 4
arguments, where `A(%r1,%r2,B)` is translated to `[r1 + A + r2 * B]`
with the constraints that `B` must be a power of two <= 8, and `A` (if
present), must be an immediate. In this case, the `72+8` and such is
constfolded by the assembler into `80`.

This commit and the previous AT&T syntax version produce the exact same
assembly output now.

src/header/setjmp/impl/i386/sigsetjmp.s

@@ -9,7 +9,7 @@ __sigsetjmp:
 
 	mov eax, dword ptr [esp + 4]
 	pop [eax + 24]
-	mov dword ptr [eax * 8 + 28], ebx
+	mov dword ptr [eax + 8 + 28], ebx
 	mov ebx, eax
 
 .hidden ___setjmp
@@ -17,8 +17,8 @@ __sigsetjmp:
 
 	push [ebx + 24]
 	mov dword ptr [esp + 4], ebx
-	mov dword ptr [esp + 4], eax
-	mov ebx, dword ptr [ebx * 8 + 28]
+	mov dword ptr [esp + 8], eax
+	mov ebx, dword ptr [ebx + 8 + 28]
 
 .hidden __sigsetjmp_tail
 	jmp __sigsetjmp_tail

src/header/setjmp/impl/x86_64/sigsetjmp.s

@@ -8,7 +8,7 @@ __sigsetjmp:
 	jz 1f
 
 	pop [rdi + 64]
-	mov qword ptr [rdi * 8 + 72], rbx
+	mov qword ptr [rdi + 8 + 72], rbx
 	mov rbx, rdi
 
 	call setjmp
@@ -16,7 +16,7 @@ __sigsetjmp:
 	push [rbx + 64]
 	mov rdi, rbx
 	mov esi, eax
-	mov rbx, qword ptr [rbx * 8 + 72]
+	mov rbx, qword ptr [rbx + 8 + 72]
 
 .hidden __sigsetjmp_tail
 	jmp __sigsetjmp_tail